The interphase interval within a bipolar nanosecond electric pulse modulates bipolar cancellation

Abstract

Nanosecond electric pulse (nsEP) exposure generates an array of physiological effects. The extent of these effects is impacted by whether the nsEP is a unipolar (UP) or bipolar (BP) exposure. A 600 ns pulse can generate 71% more YO-PRO-1 uptake compared to a 600 ns + 600 ns pulse exposure. This observation is termed "bipolar cancellation" (BPC) because despite the BP nsEP consisting of an additional 600 ns pulse, it generates reduced membrane perturbation. BPC is achieved by varying pulse amplitudes, and symmetrical and asymmetric pulse widths. The effect appears to reverse by increasing the interphase interval between symmetric BP pulses, suggesting membrane recovery is a BPC factor. To date, the impact of the interphase interval between asymmetrical BP and other BPC-inducing symmetrical BP nsEPs has not been fully explored. Additionally, interpulse intervals beyond 50 μs have not been explored to understand the impact of time between the BP nsEP phases. Here, we surveyed different interphase intervals among symmetrical and asymmetrical BP nsEPs to monitor their impact on BPC of YO-PRO-1 uptake. We identified that a 10 microsecond (ms) interphase interval within a symmetrical 600 ns + 600 ns, and 900 ns + 900 ns pulse can resolve BPC. Furthermore, the interphase interval to resolve asymmetric BPC from a 300 ns + 900 ns pulse versus 600 ns pulse exposure is greater (<10 ms) compared to symmetrical BP nsEPs. From these findings, we extended on our conceptual model that BPC is balanced by localized charging and discharging events across the membrane. Bioelectromagnetics. 39:441-450, 2018. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.

High-voltage 10 ns delayed paired or bipolar pulses for in vitro bioelectric experiments

“…Similarly, it was reported that a negative pulse three times the duration of the first caused complete loss of bipolar cancellation [10]. Moreover, the study revealed that cancellation is progressively reduced by increasing the interphase interval within the pulse [1], [4], and it can be completely reversed with a delay larger than 10 ms [8]. In addition, the delivery of two identical pulses of the same polarity (paired pulses) separated by a certain time gap was investigated.…”

“…The electrodes, modeled as perfect electric conductors, are connected through a Tee adaptor to the generator and to a 50 Ω high-voltage resistor placed in parallel to ensure impedance matching with the generator. The impedance of the electrodes delivery systems is higher than one hundred Ω [1], [8], [10], [40], [42], [43]. Thus, although the applied power is mainly dissipated in the 50 Ω resistor, the electric field applied between the electrodes is more prevalent in terms of cell perturbation.…”

“…Consistently with previous studies [2], [9], the bipolar pulse with no delay showed less YP uptake than the unipolar pulse, i.e., bipolar cancellation. Reduction of this cancellation has been observed when a delay is introduced between the two phases of the pulse, however delays of µs duration still result in less uptake than a unipolar pulse [1], [4], [8]. To our knowledge, the effect, on cells, of delays that are less than 100 ns has not previously been explored, nor has the effect of bipolar delay on pulses that have a duration of less than 300 ns.…”

“…By a delay of 110 ns this additive effect is equal to applying two positive pulses. An electrical model aiming to explain the mechanism of bipolar cancellation for pulses with typical durations between 0.1-1 µs was proposed [1], [8] [10]. The model assumes that the presence of a back pulse, opposite in polarity compared to the front pulse, determines a switch of the electrical phenomena occurring at the location of the cellular membrane.…”

“…It was shown that bipolar pulses in the nanosecond range produce cancellation of the bioeffects classically observed when applying unipolar pulses [1]- [6]. This phenomenon was largely assessed with pulse durations from 60 ns [1], [3], [7] to 900 ns [8], and more recently for 2 ns [9], for different cell lines (CHO, Jurkat, U937, or excitable cells like chromaffin cells) and for a wide range of endpoints such as YO-PRO™-1 (YP) uptake, Ca 2+ transients, cell death, calcein efflux, nerve excitation, or phosphatidylserine externalization. Cancellation with nanosecond pulsed electric fields (nsPEF) was observed with both symmetric, where the front pulse is followed by a negative polarity pulse of the same duration and amplitude [1], [4], [10] and asymmetric, where the front pulse is followed by a negative polarity pulse of different duration and/or amplitude [10].…”